The other things you find in moth traps

Limnephilus elegans – a caddisfly last recorded in 1901

Like many people I run a moth trap in the garden. It gets put out on suitable nights from March through to November. The best nights are those with low wind speeds and overcast humid conditions. Evenings with heavy rain and high winds are definite no trap days.

In the morning, hopefully, there will be a nice variety of interesting moths. Almost always though there are other things too. In the past this by-catch was carefully released in the morning but otherwise ignored. This year (2019) though I decided to try and identify as much of the by-catch as I could. By the end of the trapping season I’d amassed 300 records of 1449 individuals belonging to 64 different species.

The species caught in 2019 by taxonomic group
The species caught in 2019 by taxonomic group

Some things were not unexpected. Caddisflies (Trichoptera) are close relatives of moths, fly by night and are known to be attracted to lights. The twenty-three species caught represent 25% of the caddisfly species recorded from the Outer Hebrides. None of them were new species but some, Limnephilus vittatus, Limnephilus elegans and Limnephilus luridus had been recorded less than five times previously. These were also mostly known only from old records. The three specimens of L. elegans date from 1900 or 1901, the most recent record of L. luridus was 1962.

Nine of the seventeen species of true-flies (Diptera) were craneflies (Tipulidae) and these again are known to be attracted to light and fly at night. Quite what the three species of hoverflies were doing in the trap I don’t know. Four of the five beetles recorded were either dung beetles (Acrossus rufipes and Aphodius rufus) or sexton beetles (Nicrophorus humator and Nicrophorus investigator) and once again these are known night fliers that are attracted to light. The other beetle Otiorhynchus singularis (the Clay Coloured Weevil) is a first record for the Outer Hebrides according to the NBN Scotland Atlas.

Otiorhynchus singularis - a weevil
Otiorhynchus singularis – a weevil
Tandonia sowerbyi - Sowewrby's Keeled Slug, known previously only by a 1965 record from Barra
Tandonia sowerbyi – Sowewrby’s Keeled Slug, known previously only by a 1965 record from Barra

The five slug species are an oddity at first sight. They are unlikely to be attracted to light but the moth trap I use has a drainage hole at the bottom to allow rainwater to drain out and, apparently, to let slugs and the one species of woodlouse to get in. One of the slugs has only ever been recorded once before in the Outer Hebrides. Sowerby’s Keeled Slug (Tandonia sowerbyi) is known only by a record from Barra made in 1965.

Three species of Hymenoptera were recorded. Two of these were Ichneumons. A number of these are regularly attracted to light including the two I managed to identify (Enicospilus ramidulus and Ophion obscuratus). There were several other species of Ichneumon that I couldn’t identify but will perhaps have a more focussed effort on next year. The third hymenopteran was a sawfly (Tenthredopsis coquebertii) and this was a second NBN record for the Outer Hebrides after the previous one in 1988.

One spider, the common Garden Spider (Araneus diadematus) and a harvestman (Platybunus triangularis) were the only Arachnids identified. There were a number of smaller species I didn’t get round to doing.

Tenthredopsis coquebertii
Tenthredopsis coquebertii – only the second record
Platybunus triangularis
Platybunus triangularis

As well as the caddisflies a few other aquatic insects such as mayflies and stoneflies are attracted to lights. One of the mayflies I recorded (Caenis luctuosa) has spectacular mass emergences. On the 16th June over 300 were found in the trap and there were hundreds of others on surrounding walls and vegetation. There were smaller numbers on other dates earlier and later in June. A single individual of the second mayfly (Cloeon simile) was recorded on a single date in late June. The only stonefly was one of the small Nemouridae species (Nemoura cinerea) caught on odd occasions in April/May and again in September. An unexpected aquatic insect caught in the trap was an adult Large Red Damselfly (Pyrrhosoma nymphula) again caught in late June.

The last three groups lacewings, true bugs and barkflies were represented by single species that had one thing in common – they were all tiny. The lacewing (Micromus variegatus) was represented by two individuals recorded in July and August and hasn’t been recorded from the Outer Hebrides before. The true-bug was a leafhopper (Evacanthus interruptus) that had been previously recorded here once in 2013 at Askernish.

Caenis luctuosa - in June there are mass emergences of this species
Caenis luctuosa – in June there are mass emergences of this species
Cloeon simile - a mayfly
Cloeon simile – a mayfly
Micromus variegatus - a lacewing
Micromus variegatus – a lacewing
Evacanthus interruptus  a leafhoppe
Evacanthus interruptus – a leafhopper, only one previous record

Lastly the barkfly (Chilenocaecilius ornatipennis),  a first for the Outer Hebrides. On the NBN Atlas at the moment (22nd November 2019) there are just 10 records for the whole of the UK. The first of which dates only from 2017 and originates in Shropshire. Prior to 2015 it had only been found in Chile (as its generic name implies) and Argentina. In 2015 it was found in Cork, Ireland. In 2016 it was found in County Fermanagh though this record has yet to make it on the NBN site. It has now been found at more sites across the UK including on Orkney so there are even more records yet to make it onto the NBN Atlas sites. It seems to be spreading rapidly through the UK, presumably it was accidently imported on plants brought in from elsewhere.

Chilenocaecilius ornatipennis - first record for Outer Hebrides, only known in the UK since 2016
Chilenocaecilius ornatipennis – first record for Outer Hebrides, only known in the UK since 2016

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